This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Transcription antitermination is one of several mechanisms regulating gene expression. Non-processive antitermination, a system best characterized in bacteriophage lambda, involves structural modification of RNA polymerase (RNAP) by a complex of proteins, enabling transcription through downstream factor-dependent termination sites. The antitermination complex consists of phage protein N, N-utilization RNA control sequences (BoxA and BoxB), and at least four host proteins referred to as N-utilization substances (NusA, NusB, NusE, and NusG). Our goal is to use x-ray crystallography to analyze this complex, particularly the specific interactions between BoxA, NusB, and NusE (ribosomal protein S10) as this stable sub-complex is thought to facilitate complex assembly.